Typical flat sheet manufacturing involves the manufacturing of known sized raw rolls and sheets of flat-sheet stock. Raw flat sheet stock includes raw rolls and/or sheets and has varying widths, diameters (or length), quantity, and quality. The flat sheet stock, for example, may be steel, paper, aluminium, dry film, etc. The width and diameter (or length) of these known sized raw rolls and sheets depends on the specifications of the machines that produce them. On the other hand, customers often order product rolls and sheets that have smaller dimensions and that cannot be directly satisfied by the known sized raw rolls and sheets produced by flat sheet manufacturers. Therefore, flat sheet stock frequently must be unwound from the known sized raw rolls, cut and/or trimmed, and rewound into product rolls and/or product sheets that satisfy customer demand.
The process of cutting the larger known sized raw rolls and sheets into smaller product rolls and/or sheets as specified by customer orders is typically referred to as trimming, cutting, and/or charting, depending on the type of flat sheet industry. However, for convenience only, the term charting will be used herein to mean trimming, cutting, or charting. Alternatively or additionally, the term charting includes the determination of the necessary patterns according to which available raw rolls and sheets are processed to fill customer orders.
Charting is carried out using a set of specific equipment in various flat sheet industries. This equipment is generally referred to as secondary processing equipment, and the process of charting is generally referred to as secondary processing. Secondary processing could be implemented in either one step or multiple steps depending on the specific dimensions needed to be charted. Multiple steps are typically required due to inherent limitations of the various secondary processing equipment in terms of its capability of handling different dimensions.
Charting of raw rolls and sheet stock is currently performed manually or using in-house developed solutions to fill customer orders of different widths and diameters (or lengths). The attributes of the customer orders are typically width, diameter (or length), ordered quantity (within certain tolerances), and product type. Not all available raw rolls and sheets are usually used to fill customer orders. Therefore, the raw rolls that are available to fill any specific customer order often have varying ages (number of days to live before the stock expires).
Also, charting is typically carried out multiple times a day (e.g., a separate charting for each shift) to avoid complexity. As a result, the overall charting efficiency is poor.
Further, in the manual process, good raw rolls are charted while the defective raw rolls are not. Accordingly, generally a larger quantity of raw stock is maintained available as is necessary to fill customer orders. Thus, the cost of inventory and the waste caused by not using defective raw rolls are substantial.
On average, 10% of all manufactured raw rolls have single or multiple defects. The defect is measured as the portion of roll width along the length of the rolls. Raw roll defects are mainly of two types, major defects and minor defects. Any area of the flat sheet stock containing a major defect is not a good product and cannot be used as part of the sale. However, areas of the flat sheet stock containing a minor defect may still be good product. A defect is considered a minor defect if a cutting knife applied to an area of flat sheet stock causes a major defect in this area. Product having minor defects can be regarded as good product, and any areas containing minor defects can be part of a sale as long as a knife is not applied to the portion having the minor defect during charting.
The objective of the charting process is to minimize loss (i.e., to minimize the unused portion of raw rolls following charting) and to maximize the utilization of available stock of product and raw rolls and sheets while producing product rolls or sheets meeting customer order specifications. As mentioned above, at present charting is mostly performed manually so that the efficiency of the charting process is based on the skills of the operators.
As can be seen from the above discussion, the charting of raw rolls to fill customer orders is complex when trying to minimize loss and maximize the utilization of stock. The flat-sheet industry requires a robust, efficient, and consistent charting process for their production facilities to meet their customer demands and to improve their operational efficiency.